Sen. Chuck Grassley is demanding to know who at the Justice Department saw a memo written by a Bureau of Alcohol, Tobacco, Firearms and Explosive agent about the botched Fast and Furious gun-walking operation that was allegedly sent to the Department of Justice just one day before the agency denied that guns had crossed the U.S.-Mexico border.

In a letter to Attorney General Eric Holder on Tuesday, the Iowa Republican said the memo was forwarded to DOJ on Feb. 3, 2011, the day before the department insisted that gun-walking had not taken place as a part of Fast and Furious, which allowed thousands of guns to land in the hands of Mexican cartels. One of those guns has been linked to the death of U.S. Border Patrol agent Brian Terry.

“According to ATF personnel, the memorandum was discussed by high level ATF personnel and possibly forwarded to DOJ headquarters on Feb. 3, 2011,” Grassley, the ranking member of the Judiciary Committee, wrote. “Some individuals who spoke with my office claim they were ‘alarmed’ by the substance of the memorandum and it caused such a stir that ATF planned to put a panel together to address the allegations but someone within the DOJ suppressed the idea.”

Grassley asserted that DOJ should have been “abundantly aware” of allegations of gun-walking before it sent an “erroneous letter” to Congress on Feb. 4, and that this “raises more questions about DOJ’s claim that faulty information from Department components inadvertently led to the false letter.”

Grassley is requesting that Holder give a written response no later than July 17, providing further information about the ATF memo, including which DOJ personnel saw it on Feb 3. A DOJ spokesperson said Wednesday that the department would not comment on Grassley’s letter for the time being.

The House voted last week to hold Holder in contempt of Congress for refusing to hand over some documents in the ongoing Fast and Furious investigation.